1. Field of the Invention
This invention relates to an air discharge system for an aircraft leading edge, more particularly adapted to the leading edge of an aircraft nacelle, whereby said system makes it possible to limit the risks of separation of the air flow from the aerodynamic wall that originates in particular from the variation of the angle of attack of the aircraft and/or the orientation of wind gusts.
2. Description of the Related Art
An aircraft propulsion system comprises a nacelle in which a power plant, connected by means of a mast to the rest of the aircraft, is arranged in an essentially concentric manner.
The nacelle comprises a first wall that delimits a pipe with an air intake at the front, a first part of the incoming air flow, called primary flow, passing through the power plant to assist in the combustion, and the second part of the air flow, called secondary flow, being driven by a fan and flowing into an annular pipe that is delimited by the first wall of the nacelle and the outside wall of the power plant.
The nacelle also comprises a second so-called outside wall with essentially circular sections that extends from the air intake to the rear discharge, constituted by the juxtaposition of several elements as well as a lip, creating the air intake, connecting the first wall and the second wall.
Hereinafter, the longitudinal axis of the nacelle corresponds to the shaft of the power plant.
When the air flow entering the nacelle is oriented at a significant angle relative to the longitudinal axis of the nacelle, this creates a separation phenomenon of the air flow relative to the aerodynamic surface. This phenomenon has consequences on the proper operation of the engine. The separation of the air flow is characterized by a zone for reversal of the direction of the flow. The beginning of this zone corresponds to a line that is essentially perpendicular to the primary direction of the flow, called separation line below.
This separation phenomenon may appear both on the ground, in particular during takeoff phases by crosswind, and in flight, in particular during maneuvers with high impact at low speed.
During these phases, the separation line extends inside the air intake over a part that is more or less extended circumferentially, generally located in the upper or lateral part under stationary point or takeoff conditions and in the lower part under flight maneuvering conditions.
Thus, according to a common embodiment, the size of the nacelle as well as the thickness of the profiles of the front part of the nacelle are defined based on these operating conditions. A penalty results on the performance of the nacelle under other flight conditions, in particular during cruising.
According to the flight conditions, the wind direction on the ground, the speed and the angle of attack of the aircraft in flight or the engine speed, the position of the separation line is variable. Thus, for example, the higher the angle of attack, the closer this separation line comes to the front part (leading edge) of the air intake, while the higher the speed of the aircraft or the engine speed, the farther it moves away.
According to the document EP-1,156,962, a technique is known that makes it possible to prevent the separation of an aerodynamic flow from a wall that consists in injecting an air flow, essentially tangential to the wall, in a direction that is parallel to the aerodynamic flow, to the right or just downstream from the separation line. By adjusting the aerodynamic characteristics of the injected air flow, the risks of the separation phenomenon appearing are limited.
According to this document, the injection points of the air flow are arranged along a line that is essentially parallel to the separation line.
Consequently, as for the geometric shape, this solution for preventing the appearance of the separation phenomenon makes it possible to treat only reduced ranges of the angle of attack and the relative speed between the air flow and the aircraft.